In the past, polyolefin-based resins are supplied in a form of powder and pellets to the market. A thermal molding machine such as extruders, laminators and the like has to be used to form a film on a base material surface by a method such as coating and others when the polyolefin-based resins are used in this form. There have been such problems that melting and kneading are required when a method to melt and coat the polyolefin-based resins is used, considerable energy is required and the physical properties of the polyolefin-based resins is substantially affected by kneading.
A method for coating has then been proposed, in which the polyolefin-based resins are dissolved in an organic solvent to use as a coating solution. However, in this method, increasing a polyolefin-based resin concentration causes increase of viscosity to deteriorate coatability and is likely to give uneven thickness in the film. On the other hand, lowering the polyolefin-based resin concentration has such problems that repetitive application is required to achieve sufficient thickness.
A method to solve such problems may be considered, in which polyolefin-based resins are dispersed in a form of fine particles in water to give a dispersed solution, which is used for coating. In this case, a surface of plastics, paper, metals and the like is coated by using common coaters, printers, sprayers and the like and dried, to provide water resistivity, chemical resistivity, oil resistivity and the like to the base material. The dispersed solution above can also be used as a heat sealant. In this way, in a state of a dispersed solution above, the formation of polyolefin-based resin film becomes easier on a base material surface.
However, fine particles of polyolefin-based resins are not easy to disperse in water. For example, a dispersed solution of a water-based polyolefin wax consisting of a polypropylene wax, water and a surfactant has been disclosed (for example, see Patent Document 1). Specifically, a dispersed solution of a water-based polyolefin wax has been disclosed, which comprises a polypropylene wax with a specific average particle diameter and a specific acid value and a specific glyceride of unsaturated monocarboxylic acid. In this technique, there is a problem with flatness and smoothness of a coating film since the polypropylene wax is dispersed as a solid.
A manufacturing method of a water dispersible solution to disperse an acid-modified polyolefin in an alkaline aqueous solution is also disclosed (for example, see Patent Document 2), in which an acid-modified product of a polyethylene wax or propylene wax is used in the Example. However, in this technique, there is also a problem with flatness and smoothness of the coated film since the polyethylene wax and polypropylene wax are dispersed as a solid.
Patent Document 1: Japanese Publication of Translation of PCT No. H09-502216
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H05-156028